This program describes the use of in vivo photo-sensitization of hematoporphyrin derivative (Hpd) at surgery as an adjuvant to surgical oncology. It aims primarily at controlling locally non-resectable malignant lesions by treating residual lesions which cannot be removed surgically. Patients receive Hpd three days prior to surgery. At surgery, as much malignant tissue and involved organs or structures are removed as is possible. The residual lesions, which in most cases can be seen to fluoresce due to the presence of Hpd within the malignant lesions (a well-known property of Hpd), will be treated by the surgeon by applying light at 635nm directly to the lesions via fiber optics which are either imbedded into the tissue or used as external light sources. The light is derived from a dye-laser system producing up to 5 watts of power. Single or multiple fibers will be used as the situation dictates. Light doses of 180 to 1080 Joules will be used requiring 20-30 minutes for delivery during the surgical procedure. Since this type of therapy has already proven to be effective in eradicating a variety of superficial malignant lesions with little normal tissue damage, it is expected that the residual, potentially life-threatening lesions or portions of lesions which cannot be surgically removed and are likely to be non-responsive to chemotherapy or radiation therapy, can be eradicated by treating during the surgical procedure.